1. Field of the Invention
The present invention relates to a magneto-optical recording head comprising a magnetic head and an optical head placed in opposition; the magnetic head having a magnetic field-generating portion for applying a magnetic field locally to a magneto-optical recording medium, and the optical head having a condenser lens for focusing a light beam on a magnetic recording layer to form a light spot in a region where the magnetic field is applied. The present invention relates also to a magneto-optical recording apparatus employing the magneto-optical recording head for recording information signals.
2. Related Background Art
Magneto-optical recording apparatus are known which record information signals by applying a magnetic field modulated by the information signals onto a magneto-optical recording medium and projecting thereto a light beam for recording. FIG. 4 is a schematic side view of constitution of an example of the conventional magneto-optical recording apparatus. In FIG. 4, magneto-optical recording medium 21 is constituted of substrate 22 made of a transparent material like glass or a resin, and a magnetic recording layer 23 formed thereon, and is housed in cartridge 24. Magnetic recording layer 23 has a spiral-shaped recording track for recordation of information signals. Magneto-optical recording medium 21 is connected to a spindle motor (not shown in the drawing). Cartridge 24 has apertures. Magnetic head 25 is placed at the aperture on the upper face side (on the side of magnetic recording layer 23) of magneto-optical recording medium 21 and optical head 26 at the other aperture on the lower side thereof in opposition and with interposition of magneto-optical recording medium 21.
Magnetic head 25 comprises core 28 which is composed of a magnetic material like ferrite and has protruding columnar magnetic pole P, coil 291 surrounding the magnetic pole P, slider 30 composed of a material like a lubricative resin or ceramic, and first supporter 31 in a flat plate shape composed of an elastic material like phosphor bronze or a beryllium copper. Core 28 together with coil 29 are mounted on slider 30 such that the end face of magnetic pole P for magnetic field generation opposes magneto-optical recording medium 21. Slider 30 is fixed at the tip end of first supporter 31 and is pressed to the surface of magneto-optical recording medium 21 by the elasticity of first supporter 31.
Optical head 26 comprises laser light source 32 like a semiconductor laser, condenser lens 33, lens holder 34 for holding the condenser lens 33, second supporter 35 constituted of an elastic material like phosphor bronze or beryllium copper in a straight line shape, actuator 36 placed around lens holder 34, and basement 37 for holding these constituting members. Lens holder 34 is fixed to the tip end of second supporter 35. The base end of second supporter 35 is fixed to basement 37 which is fixed to connecting member 27. Actuator 36 is constituted of a coil and a permanent magnet which are not shown in the drawing, and drives lens holder 34 electromagnetically.
On recording the information signals, slider 30 of magnetic head 25 is pressed against the surface of magneto-optical recording medium 21, and on loading or unloading of cartridge 24, slider 30 is withdrawn upward so as not to collide with cartridge 24. Therefore, the base end of first supporter 31 is fixed to connecting member 27 at a position higher than the upper face of cartridge 24. Thus, when slider 30 is pressed against the surface of magneto-optical recording medium 21, first supporter 31 is tilted at a certain angle relative to magneto-optical recording medium 21.
Coil 29 of magnetic head 25 is connected to a magnetic head driving circuit (not shown in the drawing), and laser light source 32 of optical head 26 is connected to a laser driving circuit (not shown in the drawing), respectively.
In recordation of information signals on magneto-optical recording medium 21, firstly, magneto-optical recording medium 21 is rotated by the spindle motor. In the rotation, slider 30 of magnetic head 25 is allowed to slide on or above magneto-optical recording medium 21. Since slider 30 is pressed against the surface of magneto-optical recording medium 21, magnetic pole P of core 28 set on slider 30 can follow the displacement in the Z direction (direction perpendicular to the surface of magneto-optical recording medium 21) of the surface of the magneto-optical recording medium 21 caused by irregularity or variation in the thickness, or swing of the face of magneto-optical recording medium 21. Thereby, the interspace is kept constant between the end face of magnetic pole P of core 28 and magnetic recording layer 23 of magneto-optical recording medium 21. An electric current is applied from the magnetic head driving circuit to coil 29 of magnetic head 25 to generate a magnetic field modulated by information signals to be recorded at the end face of magnetic pole P of magnetic head 25. This magnetic field is applied virtually perpendicularly to magnetic recording layer 23 of magneto-optical recording medium 21 opposing the end face of magnetic pole P. Simultaneously, electric current is applied from the laser driving circuit to laser light source 32 of optical head 26, whereby laser light source 32 emits a light beam for recording. The emitted light beam for recording is focused by condenser lens 33 to form fine light spot S in a region of magnetic recording layer 23 of magneto-optical recording medium 21 where the magnetic field is locally applied. In the spot formation, the focusing and tracking are controlled by driving of lens holder 34 by actuator 36 so that light spot S formed by condenser lens 33 follows the displacement of magnetic recording layer 23 in the Z direction and the displacement of the recording track in the Y direction caused by the decentering of the recording medium (perpendicular to the recording track and parallel to the surface of magneto-optical recording medium 21).
Light spot S locally heats magnetic recording layer 23 to lower the coercivity at spot S to form a magnetized region in correspondence with the direction of the applied magnetic field. Thereby, information signals are recorded on the magnetic recording layer by change of the magnetization direction.
As described above, in a conventional magneto-optical recording apparatus, the surface of magneto-optical recording medium 21 deviates positionally from the prescribed level in the Z direction (direction perpendicular to the surface of magneto-optical recording medium 21) owing to irregularity or variation of the thickness, swing and so forth of the face of magneto-optical recording medium 21. The positional deviation is within the range of about xc2x1300 xcexcm. Magnetic pole P of magnetic head 25 and light spot S of the recording light beam of optical head 26 are both displaced following the displacement of magneto-optical recording medium 21 in the Z direction.
In magnetic head 25, slider 30 is held at the tip of first supporter 31 which is tilted at a certain angle relative to magneto-optical recording medium 21. Therefore, with the displacement in the Z direction, magnetic pole P of core 28 is also displaced in the X direction (parallel to the recording track within the plane parallel to the surface of magneto-optical recording medium 21). Similarly, since condenser lens 33 is held at the tip of second supporter 35 in optical head 26, light spot S of the light beam for recording is also displaced in the X direction with its displacement in the Z direction. Accordingly, with the displacement in the Z direction, the relative position of magnetic pole P to light spot S is changed in the X direction.
Since a sufficient intensity of the magnetic field for the recording is applied only in the limited region of magnetic recording layer 23 confronting the end face of magnetic pole P, light spot S should be formed within the region of magnetic field application. Accordingly, the dimension of the magnetic field application region in the X direction should be sufficiently large not to cause deviation of light spot S out of the magnetic field application region even when the relative position of magnetic pole P to light spot S varies.
The shape and size of the magnetic field application region is nearly the same as the shape and size of the end face of magnetic pole P of magnetic head 25. For the larger dimension of the magnetic field application region in the X direction, the dimension of the end face of magnetic pole P in the X direction should be increased. However, the increase of the dimension of the end face of magnetic field P of magnetic head 25 causes a proportional increase of the inductance of magnetic head 25. The larger inductance of magnetic head 25 lowers the upper limit of the modulation frequency of the generated magnetic field, lowering the speed of recording of information signals.
From the above reasons, conventional magneto-optical recording apparatus could not achieve sufficiently high speed of recording of information signals.
The present invention intends to provide a magneto-optical recording head which realizes less change of the relative position of a magnetic head to an optical head along the recording track direction when the magnetic head and the optical head are displaced the same distance in a direction perpendicular to the surface of a magneto-optical recording medium.
The magneto-optical recording head of the present invention comprises a magneto-optical recording head comprising a magnetic head for applying a magnetic field to a magneto-optical recording medium, an optical head placed with interposition of the recording medium in opposition to the magnetic head for projecting a light spot through a condenser lens onto the region to which the magnetic field is applied, a first supporter for supporting the magnetic head, and a second supporter for supporting the condenser lens; wherein displacement of relative positions of a magnetic field-generating portion of the magnetic head and the light spot in a horizontal direction parallel to a surface of the recording medium caused by displacements of the magnetic field-generating portion of the magnetic head and the light spot in a direction perpendicular to a surface of the recording medium is smaller than a displacement of the magnetic field-generating portion in the horizontal direction parallel to the surface of the recording medium.
The magneto-optical recording apparatus of the present invention employs the above magneto-optical recording head.